(355g) Decoupling Mechanical Properties and Ion Conductivity in Supramolecular Stretchable Battery Materials

As soft electronic devices increasingly require stretchable, conformable batteries, safety concerns regarding the use of liquid electrolytes in lithium ion batteries (LIBs) arise. Unfortunately, the canonical tradeoff between mechanical strength and ionic conductivity in polymer electrolytes has forced most reported stretchable batteries to incorporate mechanically weak electrolytes containing flammable liquids within strain engineered structures. Herein, we introduce a supramolecular design as a novel strategy to decouple ionic conductivity from mechanical strength in polymer electrolytes. The supramolecular lithium ion conductor (SLIC) is a block copolymer that includes a hydrogen-bonding domain based on 2-ureido-4-pyrimidone (UPy) and an ion conducting domain based on poly(propylene glycol)-poly(ethylene glycol)-poly(propylene glycol) (PPG-PEG-PPG). By systematically tuning the amount of UPy in the polymer backbone of SLIC, we demonstrate that the UPy domains and the PPG-PEG-PPG domains are orthogonally functional, and that varying the amount of UPy in the backbone has little effect on the ionic conductivity of the polymer. The resulting SLIC polymer containing 23 mol.% UPy in the backbone yields a polymer electrolyte with high resilience (4.9 MJ m^-3) and high ionic conductivity (1.2*10^-4 S cm^-1 at 25° C ). Implementation of SLIC as a binder material allows for the creation of stretchable Li-ion battery electrodes with strain capability of over 900% via a conventional slurry process. Impressively, strain capability of 100% is maintained when the loading of polymer in the electrode film is as low as 20 wt.%. The supramolecular structure of SLIC allows for intimate bonding at the electrode-electrolyte interface. Good adhesion between the stretchable battery components enables the fabrication of the first intrinsically stretchable LIB. The SLIC battery has a capacity of 1.1 mAh cm^-2, an operating voltage of 1.8 V, and functions even when stretched to 70% of its original length. The method reported here of decoupling ionic conductivity from mechanical properties opens a new route to create highly resilient ion transport materials for energy storage applications.